People who survive six months or longer after suffering traumatic brain injuries continue to remain at risk for premature death long after their injury, according to a study published Wednesday by the American Medical Association.

The study, led by Dr. Seena Fazel at the University of Oxford in England, used data from Sweden going back to 1954. With data from such a long time period, the research team was able to draw conclusions about the long-term consequences of moderate to severe traumatic brain injuries, Fazel said.

“One of the bottom lines is thinking about this as a chronic illness, a chronic disease,” he said.

His team found that while traumatic brain injuries, or TBI, tend to be one-off events, they have chronic, long-term consequences, he said. “And one of the consequences is premature mortality.”

The risk of premature death after a TBI is small — just 3.6 percent, according to the study. But among those who survived six months or longer after a TBI, there was a threefold increase in the odds of dying early when compared to the general population, according to the study. The odds of early death jump even higher for TBI patients also suffering from psychiatric illnesses, depression or substance abuse.

“The co-morbidity seems to elevate risks really substantially,” Fazel said. “For instance, if you have TBI and psychiatric illness, your odds of suicide before the age of 56 are increased 19-fold.”

About half of the early deaths noted in the study resulted from external factors, such as suicide, accidents and other injuries. The other half came from a range of other conditions, such as heart disease and cancer. However, Fazel said the study was not designed to draw conclusions about why there is such a correlation between TBI and early death.

Asked about what the study means for military personnel who have suffered TBIs, Fazel said he hoped TBI patients would be more likely to seek assessment or treatment if they know they’re at increased risk for depression or other ailments developing after a TBI.

“In a way, it’s about coming to terms with the changes and being aware of what are some of the possible consequences going forward.”